Pittsburgh Mayor Bob O'Connor stands to lose his white hair and suffer some scalp irritation as a result of recent whole-brain radiation therapy, but the treatment should reduce or eliminate the four masses of lymphoma, according to one expert.

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"The tumors did not appear overnight and they will not disappear overnight, but you could see improvements as early as one week," said Dr. Carol L. Kornmehl, medical director of radiation oncology at Passaic Beth Israel Regional Medical Center in Passaic, N.J., and author of the 2004 book, "The Best News About Radiation Therapy."

She said the primary central nervous system T-cell lymphoma that Mr. O'Connor was diagnosed with last month typically does not always respond well to chemotherapy but is sensitive to radiation treatment.

Mr. O'Connor underwent two whole-brain radiation treatments last week, then began daily treatments of intensity-modulated radiation therapy at about 10 a.m. yesterday, with plans for IMRT treatments to continue for four weeks, said Clare Collins, spokeswoman for University of Pittsburgh Medical Center.

IMRT is a method of pinpointing tumors with powerful and precise beams of radiation without affecting healthy tissue.

Ms. Collins said the treatment took about a half-hour and Mr. O'Connor "tolerated it well." He remains in stable condition at UPMC Shadyside.

Mayoral spokesman Dick Skrinjar said he visited the mayor over the weekend and found him in good spirits.

"He would have been in a better mood if the Steelers had won," he said.

He said the mayor was up on the edge of his bed and was doing physical therapy. "He sounded good to me," Mr. Skrinjar said. "He was Bob O'Connor."

Mr. O'Connor, he said, was happy with an inspection sweep in Oakland Friday that resulted in 270 property owners being cited for property maintenance violations.

"He was quite pleased with that. He loved the idea of being proactive," he said, adding it sent a good message to students moving in and their parents that Pittsburgh was a clean and safe city.

While undergoing radiation treatment, Mr. O'Connor also underwent a second procedure last week to reduce buildup of fluids in the brain, leading to improvements in his symptoms over the weekend.

If all goes ideally with treatments, Mr. O'Connor could have a normal magnetic resonance image or MRI of his brain in four weeks, Dr. Kornmehl said.

More realistically, she said, the four lymphoma masses in his brain will be reduced significantly, with about a 50 percent chance of a normal MRI when treatments end in mid-September.

After his diagnosis last month, Mr. O'Connor underwent chemotherapy, but last week his team of doctors said it had not produced desired results, prompting radiation therapy.

Dr. Kornmehl said IMRT uses MRI and CAT scans to program equipment to send precise beams of radiation of different intensities to tumors without damaging contiguous tissue.

Because precision is required in the mosaic of radiation beams, it takes "hours and hours" to prepare the program to protect the optic nerve, brain stem and other areas of the brain from radiation damage, she said.

"You modulate the radiation beam to give higher doses to some areas and lower doses to other areas," she said. "You modulate the beams and make them match the shape of the tumor."

The course of treatment that included chemotherapy, then whole-brain radiation last week before proceeding with IMRT this week, is a proper routine for the T-cell lymphoma that Mr. O'Connor has, she said.

Whole-brain radiation was necessary last week, she said, because of the preparation time required for IMRT.

"You don't know for sure, but T-cell lymphoma is usually sensitive to radiation," Dr. Kornmehl said. "That means he should have a good outcome."